javascript - 如何因超时而停止轮询？

Question

所以我正在投票一些非常标准的东西

(function poll(){
    $.ajax({ ... })
});

...效果很好。但现在，我希望能够继续每隔几秒轮询一次，如果两分钟后没有得到响应，则停止轮询并引发错误。

如何实现超时？

Answer 1

这样的事情怎么样？在 ajax promise 内初始化、跟踪和重置轮询。

var pollingTimer     = null, // stores reference to the current timer id
    firstTimeoutResponse = null; // stores the start of what might be a series of timeout responses

function poll(){
  $.ajax({
    // your options here...
  }).done(function() {
    // reset the "timeout" timer
    firstTimeoutResponse = null;
  }).fail(function(jqXHR, textStatus) {
    // if the failure wasn't a timeout, short-circuit, 
    // but only after resetting the timeout timestamp
    if (textStatus !== 'timeout') {
      firstTimeoutResponse = null;

      return;
    }

    // if it was a timeout failure, and the first one (!), init the timeout count
    if (firstTimeoutResponse = null) { 
      firstTimeoutResponse = (new Date).getTime();
    }
  }).always(function() {
    // if 2 min have passed and we haven't gotten a good response, stop polling/chort-circuit
    if ((new Date).getTime() - firstTimeoutResponse > 120000) { // 120000ms = 2min
      window.clearTimeout(pollingTimer);

      return;
    }

    // queue the next ajax call
    pollingTimer = window.setTimeout(poll, 3000); // poll every 3s
  });
}

// kick things off!
poll();